This invention relates generally to coils or inductors which are used in various electrical or electronic circuits, and particularly, the present invention relates to lamination-wound chip coils and method for manufacturing the same.
Most conventional coils, which are used in electrical or electronic circuits formed on a printed circuit board, have a magnetic core and a winding wound around the core. Both ends of the winding are respectively connected to lead wires which extend externally. However, such conventional coils have drawbacks in that it is troublesome and time-consuming to wind the winding, and it is bulky. Since it is preferred that various electrical and electronic parts and elements be small in size so as to fit in a limited space on a printed circuit board, it has been desired to develop a small coil chip. Furthermore, conventional coils required relatively long periods for mounting the same on a printed circuit board because the lead wires have to be bent, as facebonding techniques could not be applied.
Recently, a new type of coil has been developed as disclosed in Japanese Utility model Provisional Publication No. 55-108717. According to this new type of coil, a conductor strip is attached to one surface of an elongate magnetic sheet, and then the lamination of the magnetic sheet and the conductor strip is wound up to form a roll. The conductor strip is S-shaped or crank-shaped so that both ends of the strip will be exposed on both sides of the roll. Suitable metal terminals are then attached to both sides of the roll.
Although drawbacks inherent to the conventional coils can be solved by the above-mentioned new type coil, which may be called lamination-wound type coil, this lamination-wound coil has a drawback that the inductance range is relatively small because the inductance of the coil to be produced is defined by only the length of the conductor strip when the materials of the conductor strip and the magnetic sheet are not changed. Furthermore, the lamination-wound type coil disclosed in the above publication is apt to suffer from cracks which occur due to delamination or loose winding. In addition to these drawbacks, the lamination-wound coil is difficult to manufacture because it is difficult to tightly wind the lamination to form a roll.